Off the top of my head, IDW hasn't yet used the PD movies, Welsh magazine, the 2007 movie and its toyline, the US comic strip, Coming Out of Their Shells, the terrible VHS specials, the myriad original kids books, and maybe the video games. What else have they not used yet?

EDIT: Though not specifically characters, the following have been used for plot points: Image (Don as Metalhead) & The Next Mutation (Raph’s Motorcycle). The following have been used for Easter Eggs: 90s movies, 1988-1997 Playmates Toys (unless one counts the myriad characters that started there but showed up in Archie and Fred Wolf).

Edit: Don's "death" is taken from Vol. 3, thanks CyberCubed.

Edit: NOTE: International productions, like "Las Tortugas Ninjas", Legend of the Supermutants, the Fleetway comic, the Titan comic, Il Giornalino, etc. don't really count, due to the international copyright laws. Regardless, if you have suggestions for stuff from those versions, please discuss that here.

Edit: Raphael stealing a motorcycle may be a tip of the hat to Next Mutation.

Edit: An Easter egg of Jordan Perry has appeared, much like the Easter egg of a few toyline characters.

Don as Metalhead with a smashed shell is likely a homage to cyborg Don from Image. Even if it might not have been intentional, its very similar. Don gets his shell smashed and wakes up as a cyborg turtle? And they advertise that Don is "dead" which is the same thing the Image run did when they made it seem like he died.

I'd kinda like to see 2007's Winters as an initial antagonist whose goals are well-intentioned that they save from himself, who becomes a sometimes ally when dealing with corporations or high-society corruption, or someone who can help them cross countries under the guise of his historical/excavational interests.

__________________
If you can't take your 'Ninja Turtles' with a knowing wink and a smile on your face then what have you got left?

I might be wrong but they haven't used anything from the first two live-action movies, they have some things unique to them like Shredder's warehouse of delinquent kids, Tatsu (who can't be used by IDW anyway), Shredder and Splinter attacking and scarring each other after Yoshi's death, Tokka and Rahzar, Dr. Perry, Raph being beaten into a coma, etc.

I'm not sure if the same goes for the third movie, that has some unique things too like the mass transference thing where the samurai and Turtles swap places, or Lord Norinaga, or Casey's ancestor.

The only thing they'll probably take from any of the movies at some point is Rahzar/Tokka. They already said they can't use Tatsu. And we certainly don't need to see anything from the Michael Bay movies like Eric Sachs.

I know technically every incarnation of tmnt takes from mirage but I really wish this one would more...particularly later stuff that's more unique to mirage. Like the survivalists and river arcs and radical

I know technically every incarnation of tmnt takes from mirage but I really wish this one would more...particularly later stuff that's more unique to mirage. Like the survivalists and river arcs and radical

Yeah, survivalists and the River trilogy would both be good, but maybe if TMNT Universe went back and showed them as part of the Northampton story...

Neither of those stories would fit in very well in New York, and I don't see the guys heading to the country anytime soon.

And I've never understood why people like Radical, or the Justice Force, or any of the Mirage "supers." Ugh. Give 'em all capes and tell them to ignore Edna Mole's advice.

I know technically every incarnation of tmnt takes from mirage but I really wish this one would more...particularly later stuff that's more unique to mirage. Like the survivalists and river arcs and radical

In mirage they spent way more time in North Hampton and went back and forth regularly. Survivalists would work if they did that more, hell I'm sure the writers could think of a reason to have the turtles go upstate. Have you guys ever been 30 minutes North of Manhattan? Survivalists is super relevant today! There's a lot of real life groups like that especially in upstate NY.

As for radical..I would have said the mutanimals would never work in idw before they were totally reimagined. The same could be done for radical.